It is often desirable to utilize wireless radio links to provide information communication. The use of wireless links may be advantageous where wired infrastructure (e.g., copper and/or fibre communication network) is not in place to provide information communication or where user demand, whether the number of users and/or the capacity required by users, does not make it economical to provide wired infrastructure. For example wireless local loop (WLL) is often thought of to provide voice services in places where wireline service is not available, such as in less developed countries and remote areas within the United States.
In addition to providing voice services to remote sites not otherwise provided wireline service, it may also be desired to use radio to provide high rate data services to fixed users where wireline service is inadequate or not available. However, a problem with providing high rate data services, such as 1 MB/s, is that RF spectrum is limited and expensive. For example, to attain high peak rates often required or desired by data systems, spectrum bandwidth on the order of 1 MHZ is typically required. Spectrum in the 1-3 GHz range may be utilized to attain high peak rates such as 1 MB/s. Such frequencies may also be suitable for use in providing data system communication as their frequency propagation conditions typically allow partial line-of-sight or even non-line-of-sight between a base station (BS) and a remote station (RS), thus simplifying deployment of a network.
Although possibly providing suitable spectrum for data system communications, spectrum in the 1-3 GHz range is becoming widely used for a range of wireless communications. This results in both the spectrum being expensive as well as potentially having a high level of noise energy, caused by multiple uses of the
At millimeter wave (mm-wave) frequencies a great deal of spectrum is available. However, such frequencies have disadvantages associated with their use. For example, mm-wave propagation is typically limited to line-of-sight between a BS and a RS. Additionally, mm-wave radio propagation is severely limited by rain and terrain, requiring complex control systems to deal with temporary rain fades or increased transmit power to allow for a worst case scenario. Such increase power, in addition to the obvious expense in such a brute force solution, can limit reuse of frequencies because of the overlapping radiation patterns experienced when the conditions requiring the increased power are not present or are not fully present in a particular antenna beam. Nevertheless, multibeam antennas can provide benefit to this frequency band.
There are some lower frequencies where spectrum is still available. For example, there is unused personal communications services (PCS) spectrum and under utilized ultra-high frequency (UHF) television channel spectrum available in many geographic regions of the United States. Additionally spectrum associated with multichannel multipoint distribution service (MMDS), 200 MHZ bandwidth at 2.5 GHz, remains available in many areas. These portions of the spectrum often remain under/un-utilized because of the inability of service providers to efficiently and economically allocate the spectrum for use to multiple users.
In order to provide the desired data rate (data bandwidth) in the available spectrum to multiple users in an efficient and economical manner, it is advantageous to reuse frequencies. The reuse of frequencies in wireless systems has been done in cellular communication systems, where a plurality of BSs are allocated particular frequencies or ranges of frequencies to provide communications in an associated service area and where adjacent BSs or portions thereof are restricted from use of same frequencies. The use of narrow antenna beams in cellular systems can provide capacity gains of 100% or more, compared to ordinary sectorized cellular systems. However, the spectral reuse efficiency is still less than 25%, i.e., at most 25% of the spectrum is available for use at a single sight.
Code division multiple access (CDMA) cellular systems can reuse the spectrum 3 times at a cell sight. However, CDMA communications are quite inefficient in throughput. For example, one CDMA sector typically provides only 100 kbs (15 walsh codes×13 kbls) while using at least 1.5 MHZ bandwidth.
To make the best use of such frequencies, what is needed in the art is a robust, spectrally efficient system and method to provide voice and high rate data on demand to multiple geographically dispersed users.